diff --git a/keyserver/src/push/send.js b/keyserver/src/push/send.js
--- a/keyserver/src/push/send.js
+++ b/keyserver/src/push/send.js
@@ -435,6 +435,7 @@
   };
 
   for (const userID in usersToCollapsableNotifInfo) {
+    missingUserIDs.add(userID);
     for (const notifInfo of usersToCollapsableNotifInfo[userID]) {
       for (const rawMessageInfo of notifInfo.existingMessageInfos) {
         addUserIDsFromMessageInfos(rawMessageInfo);